The present invention relates to a technology to stabilize a curtain coater employing a curtain coating method, and in particular, to a technology to form a curtain layer stably.
There has been known a curtain coating method wherein a coating solution flowing down along a slide surface of a coater die in a form of a uniform layer is caused to fall from a tip of a die lip of the coater die to be formed into a thin curtain layer of coating solution which is, then, put continuously on a web of a long support while the support is running at a certain high speed for coating. In a coating apparatus manufacturing a light-sensitive material by the use of the curtain coating method mentioned above, it is very important that a curtain layer is formed in a stable manner. It has been cleared that a teapot phenomenon is remarkable, and that phenomenon sometimes caused a curtain layer not to be formed at a bottom end portion of an edge guide (skipped curtain layer) especially in a system wherein a quantity of a coating solution is large. The teapot phenomenon is one wherein with regard to a coating solution which flows down along the slide surface and is just about to fall from the tip of a die lip, a curtain layer does not fall in the vertical direction due to a flow speed of coating solution varying at each point in the direction of a flowing layer thickness, but it falls while it is curved toward the die. Various inventions which will be stated below have been achieved, for improving the skipped curtain layer mentioned above.
Namely, Japanese Patent Publication Open to Public Inspection No. 99668/1989 (hereinafter referred to as Japanese Patent O.P.I. Publication) discloses a means to strengthen and stabilize a curtain layer by causing side solutions to flow additionally on end portions at both sides for improving the foregoing by preventing the skipped curtain layer. In this means, however, the side solution is accumulated on each end portion intensively, resulting in an excessive thick layer on each of both sides, although the curtain layer is not skipped.
For the intent of inhibiting the increase in a layer thickness on each side, a thick layer portion on an end portion of a curtain layer is removed through attraction, as disclosed in Japanese Patent O.P.I. Publication Nos. 477/1986 and 233954/1994.
In Japanese Patent O.P.I. Publication No. 57734/1976, a curtain layer is stabilized by the use of a flat plate type edge guide. However, even this method can not solve the phenomenon of thick layers at both edges.
(Problems to be solved by the invention)
In the case of the means to strengthen and stabilize a curtain layer by causing side solutions to flow on edge portions of both sides as stated above, side solutions are accumulated intensively at edge portions on both sides of a coating surface, resulting in increased layer thickness at both sides which applies greater load on a drying process.
When taking a means of attraction on both sides as stated above for solving the problem mentioned above, an expense for installation of facilities and a load for maintenance expense are increased, and a cost of coating solutions equivalent to those removed at end portions is also increased.
Further, separately from the foregoing, when using the flat plate type edge guide, it stabilizes a curtain layer no doubt, but a layer thickness on the side of a curtain layer is increased to create a thick layer because an area of contact between the flat plate type edge guide and a coating solution is increased, which results in greater load on a drying process and in reduction in an effective width for a product.
Namely, as far as the inventions mentioned above are concerned, a curtain layer can be stabilized to a certain extent, but an area of contact between a coating solution and an edge guide is increased and edge portions are made to be uneven accordingly, in any case of the inventions mentioned above. Therefore, a load for drying thick layer portions is caused and sufficient uniform coating necessary for products can not be obtained, and in spite of the insufficient effect, installation of facilities and actions for the effect are needed, which has resulted in an increase in expenses. Accordingly, it has been required a method wherein the relation of the state of contact between an edge guide and a coating solution is investigated and a curtain layer can be stabilized.